CVE-2021-27905
CriticalThe ReplicationHandler (normally registered at "/replication" under a Solr core) in Apache Solr has a "masterUrl" (also "leaderUrl" alias) parameter that is used to designate another ReplicationHandler on another Solr core to replicate index data into the local core.
Published Jul 9, 2021 · Updated Sep 8, 2026 · Also known as BIT-solr-2021-27905, DEBIAN-CVE-2021-27905, GHSA-5phw-3jrp-3vj8, TR-21-0317, UBUNTU-CVE-2021-27905
Key Facts
Patch immediately- CVE-2021-27905 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting Solr (Apache), lucene-solr (debian), org.apache.solr:solr-parent (maven).
- It is not listed in any known-exploited vulnerabilities catalog. No public exploit code is known.
- EPSS estimates a 93% probability of exploitation in the next 30 days.
- Fixed versions are available, including Solr 8.8.2, Solr 8.8.2-1, lucene-solr 3.6.2+dfsg-23.
- Brandefense priority: patch immediately, because it is very likely to be exploited soon.
CVSS v3.1
9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
93%
Higher than 99.8% of all scored CVEs
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
None known
Get the full CVE-2021-27905 brief as a PDF
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Description
The ReplicationHandler (normally registered at "/replication" under a Solr core) in Apache Solr has a "masterUrl" (also "leaderUrl" alias) parameter that is used to designate another ReplicationHandler on another Solr core to replicate index data into the local core. To prevent a SSRF vulnerability, Solr ought to check these parameters against a similar configuration it uses for the "shards" parameter. Prior to this bug getting fixed, it did not. This problem affects essentially all Solr versions prior to it getting fixed in 8.8.2.
Affected Products
24 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| SolrApache | >= Apache Solr | 8.8.2 |
| lucene-solrdebian | See advisory | 3.6.2+dfsg-23 |
| org.apache.solr:solr-parentmaven | See advisory | 8.8.2 |
Patched Releases
Solr
8.8.2, 8.8.2-1
lucene-solr
3.6.2+dfsg-23
org.apache.solr:solr-parent
8.8.2
Timeline
Publicly disclosed
Jul 9, 2021
Last updated
Sep 8, 2026
Weakness Type
- CWE-918 Server-Side Request Forgery (SSRF)
References
- advisoryhttp://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-4590
- advisoryhttps://exchange.xforce.ibmcloud.com/vulnerabilities/184650
- advisoryGHSA advisory
- advisoryhttps://lists.apache.org/thread.html/r0ddc3a82bd7523b1453cb7a5e09eb5559517145425074a42eb326b10%40%3Cannounce.apache.org%3E
- advisoryhttps://nvd.nist.gov/vuln/detail/CVE-2021-27905
FAQ
Common Questions.
The ReplicationHandler (normally registered at "/replication" under a Solr core) in Apache Solr has a "masterUrl" (also "leaderUrl" alias) parameter that is used to designate another ReplicationHandler on another Solr core to replicate index data into the local core.
Affected: Solr (Apache) versions >= Apache Solr; lucene-solr (debian); org.apache.solr:solr-parent (maven). The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
Fixed versions are available, including Solr 8.8.2, Solr 8.8.2-1, lucene-solr 3.6.2+dfsg-23.
Brandefense priority: patch immediately, because it is very likely to be exploited soon.
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